Senses

1. Senses • Sense: ability to perceive stimuli • Sensation: conscious awareness of stimuli received by sensory neurons • Sensory receptors: sensory nerve endings that respond to stimuli by developing action potentials

2. Types of Senses • Generalsenses: - receptors over large part of body - somatic provide info. about body and env’t - visceral provide info. about internal organs, pain, pressure - touch, pressure, pain, temp., and itch • Special senses: smell, taste, sight, hearing, and balance

3. Types of Receptors • Mechanoreceptors: - detect movement - Ex. touch, pressure, vibration • Chemoreceptors: - detect chemicals - Ex. Odors • Photoreceptors: detect light

4. Thermoreceptors: detect temp. changes • Nociceptors: detect pain

5. Types of Touch Receptors • Merkel’s disk: detect light touch and pressure • Hair follicle receptors: detect light touch • Meissner corpuscle: - deep in epidermis - localizing tactile sensations

6. Ruffini corpuscle: - deep tactile receptors - detects continuous pressure in skin • Pacinian corpuscle: - deepest receptors - associated with tendons and joints - detect deep pressure, vibration, position

7. Figure 9.1

8. Pain • What is it? unpleasant perceptual and emotional experience

9. Types of Pain • Localized: - sharp, pricking, cutting pain - rapid action potential • Diffuse: - burning, aching pain - slower action potentials

10. Pain Control • Local anesthesia: - action potentials suppressed from pain receptors in local areas - chemicals are injected near sensory nerve • General anesthesia: - loss of consciousness - chemicals affect reticular formation

11. Referred Pain • What is it? - originates in a region that is not source of pain stimulus - felt when internal organs are damaged or inflamed - sensory neurons from superficial area and neurons of source pain converge onto same ascending neurons of spinal cord

13. Olfaction • What is it? • - sense of smell • - occurs in response to • odorants • - receptors are located • in nasal cavity and • hard palate • - we can detected • 10,000 different smells

14. How does olfaction work? • Nasal cavity contains a thin film of mucous where odors become dissolved. • Olfactory neurons are located in mucous. Dendrites of olfactory neurons are enlarged and contain cilia. 3. Dendrites pick up odor, depolarize, and carry odor to axons in olfactory bulb (cranial nerve I). 4. Frontal and temporal lobes process odor.

15. Figure 9.3b

16. Taste • Taste buds: - sensory structures that detect taste - located on papillae on tongue, hard palate, throat • Inside each taste bud are 40 taste cells • Each taste cell has taste hairs that extend into taste pores

17. Figure 9.4

18. How does taste work? • Taste buds pick up taste and send it to taste cells. • Taste cells send taste to taste hairs. • Taste hairs contain receptors that initiate an action potential which is carried to parietal lobe. • Brain processes taste.

19. Types of Tastes • Sweet • Sour • Salty • Bitter • Umami • Certain taste buds are more sensitive to certain tastes. • Taste is also linked to smell.

20. Vision Accessory Structures • Eyebrow: - protects from sweat - shade from sun • Eyelid/Eyelashes: - protects from foreign objects - lubricates by blinking

22. Conjunctiva: thin membrane that covers inner surface of eyelid • Lacrimal apparatus: produces tears • Extrinsic eye muscles: help move eyeball

24. Figure 9.8

26. Anatomy of Eye • Hollow, fluid filled sphere • Composed of 3 layers (tunics) • Divided into chambers

27. Fibrous Tunic • Outermost layer • Sclera: - firm, white outer part - helps maintain eye shape, provides attachment sites, protects internal structures • Cornea: - transparent structure that covers iris and pupil - allows light to enter and focuses light

28. Vascular Tunic • Middle layer • Contains blood supply • Choroid: - black part (melanin) - delivers O2 and nutrients to retina • Ciliary body: helps hold lens in place • Suspensory ligaments: help hold lens in place

29. Lens: - flexible disk - focuses light onto retina • Iris: - colored part - surrounds and regulates pupil • Pupil: - regulates amount of light entering - lots of light = constricted - little light = dilated

31. Figure 9.10

32. Nervous Tunic • Innermost tunic • Retina: - covers posterior 5/6 of eye - contains 2 layers • Pigmented retina: - outer layer - keeps light from reflecting back in eye

33. Sensory retina: - contains photoreceptors (rods and cones) - contains interneurons • Rods: - photoreceptor sensitive to light - 20 times more rods than cones - can function in dim light • Cones: - photoreceptor provide color vision - 3 types blue, green, red

34. Figure 9.12b

35. Figure 9.12c

36. Rhodopsin: photosensitive pigment in rod cells • Opsin: colorless protein in rhodopsin • Retinal: - yellow pigment in rhodopsin - requires vitamin A

37. Effects of Light on Rhodopsin • Light strikes rod cell • Retinal changes shape • Opsin changes shape • Retinal dissociates from opsin • Change rhodopsin shape stimulates response in rod cell which results in vision • Retinal detaches from opsin • ATP required to reattach retinal to opsin and return rhodopsin to original shape

38. Figure 9.13

39. Retina Structures Continued • Rods and cones synapse with bipolar cells of sensory retina • Horizontal cells of retina modify output of rods and cones • Bipolar and horizontal cells synapse with ganglion cells • Ganglion cells axons’ converge to form optic nerve

40. Nervous Tunic (Retina) • Innermost layer • 2 parts of retina: sensory and pigmented • Keeps light from reflecting back into eye • Rods: photoreceptors that detect amount light • Cones: - photoreceptors that detect colors - 3 types: red, blue, green

41. Macula: small spot near center of retina • Fovea centralis: - center of macula - where light is focused when looking directly at an object - only cones - ability to discriminate fine images

42. Optic disk: - white spot medial to macula - blood vessels enter eye and spread over retina - axons exit as optic nerve - no photoreceptors - called blindspot

44. Chambers of Eye • Anterior chamber: - located between cornea and lens - filled with aqueoushumor (watery) - aqueous humor helps maintain pressure, refracts light, and provide nutrients to inner surface of eye • Posterior chamber: - located behind anterior chamber - contains aqueous humor

45. Vitreous chamber: - located in retina region - filled with vitreous humor: jelly-like substance - vitreous humor helps maintain pressure, holds lens and retina in place, refracts light

46. Functions of Eye Light Refraction Bending of light • Focal point: - point where light rays converge - occurs anterior to retina - object is inverted

47. Focusing Images on Retina • Accommodation: - lens becomes less rounded and image can be focused on retina - enables eye to focus on images closer than 20 feet

49. Neuronal Pathway for Vision • Optic nerve: leaves eye and exits orbit through optic foramen to enter cranial cavity • Optic chiasm: where 2 optic nerves connect • Optic tracts: route of ganglion axons

50. Figure 9.16b